canonicalize_url inappropriately "lowercases" credentials (username/password) in url

```python
from w3lib.url import canonicalize_url


def main():
    url = "sftp://USERNAME:ABC@domain.com"

    print(canonicalize_url(url))
    print(canonicalize_url(url) == url)

``` 

```
sftp://username:abc@domain.com/
False
```